A gas insulated switchgear has a structure in which an open/close portion composed of a vacuum valve and the like is fixed in a pressure tank filled with a gas that is excellent in insulation property and arc-distinguishing capability. In general, this pressure tank is filled with the gas at a pressure of about 0.03 to 0.6 MPa, and as compared to a conventional air insulated switchgear, excellent insulation property and excellent arc-distinguishing capability are obtained and significant downsizing is achieved. In addition, since the open/close portion is sealed in the pressure tank, the open/close portion is not subject to contamination, and thus high reliability and safety are obtained.
In this gas insulated switchgear, it is necessary to stably retain the gas in the pressure tank and prevent the pressure tank from being broken due to stress concentration on a corner portion of the pressure tank by the internal pressure of the filling gas. In order to adapt to such a purpose, the pressure tank is configured such that wall surface materials formed from metal plates are combined, connection parts of the wall surface materials are connected by welding, and further, a rod-like member or a bent plate material is welded to the inner wall surface of the pressure tank, for reinforcement (for example, Patent Document 1 and Patent Document 2).
In general, as a structure for enhancing the strength of a container such as a tank, there is known a structure in which a plate-shaped reinforcing member is formed between the opposed ones of the wall surface materials composing the tank and thus a wall is formed in the tank (for example, Patent Document 3). For joining between the plate-shaped reinforcing member and the wall surface materials, protruding tenon portions are formed on two opposed sides of the plate-shaped reinforcing member, and the opposed wall surface materials have slit-like mortises into which the tenon portions are inserted and which penetrate through the wall surface materials. From inside of the tank, the tenon portions formed on the two sides of the reinforcing member are inserted and fitted into the mortises of the two opposed wall surface materials, and the tenon portions and the mortises are welded from outside of the tank, whereby the plate-shaped reinforcing member can be fixed between the opposed wall surface materials in the tank.